Idukki Dam

Idukki Dam is India's tallest arch dam — a 168 m concrete double-curvature arch dam spanning the Periyar river gorge at Idukki in Kerala's Western Ghats. Completed in 1976, the dam is the keystone of the Idukki Hydroelectric Project — Kerala's largest hydropower complex with 780 MW installed capacity.

The project comprises three dams in cascade: the main Idukki Arch Dam, the smaller Cheruthoni Concrete Gravity Dam (138 m × 651 m), and the Kulamavu Dam (100 m × 385 m). Together they impound the Idukki Reservoir at full storage 1.96 cubic km. Water from the reservoir is fed via 5 km of pressure tunnels to the Idukki Underground Power House — among the largest underground power complexes in India.

Idukki was constructed by Kerala State Electricity Board (KSEB) between 1969 and 1976 with extensive Canadian technical assistance under the Colombo Plan. Construction was challenging due to the Periyar's steep gorge geometry and Kerala's heavy monsoon — the foundation excavation alone took 4 years.

The arch dam's double-curvature design (curved both horizontally + vertically) was a state-of-the-art choice in 1970s India, allowing thinner concrete cross-sections and significant material savings vs traditional gravity dams. The dam-arch reflects this in its iconic curved profile.